Previously, cylinders that can be extended with hydraulic pressure or compressed air are known as power units that can be telescopically extended. The purpose of use of these units is mostly lifting, in which case the recovery of the cylinder to be short occurs with the help of gravitational force by letting the pressure out of the cylinders. If gravitational force and removal of the pressure cannot be used to pull this kind of cylinder back to be short, mechanical pulling devices, such as withdraws occurring with a wire draw are known.
From a Chinese publication CN 2809309Y telescopic parts equipped with threads that are needed for uplifting of a lifting platform construction are known, in which telescopic parts can be extended and shortened in relation to each other by rotating. In this construction the telescopic parts are made of metal and they are considerably heavy. In order to avoid excessive increase of the weight, the telescopic parts have as small a diameter as possible. In order to function, one such power unit requires yet the fact that at least one telescopic part be locked to be non-rotating. A construction with a size of a power unit will thus increase the weight of the construction. When the telescopic parts are made to have small diameters in order to save weight, the construction will buckle easily if one tries to achieve great endurance of the load and lifting height or great elongation with it.